This invention relates to a fluid displacement apparatus of the scroll type, such as a compressor, expander or pump.
Scroll type fluid displacement apparatus are well-known in the prior art. For example, U.S. Pat. No. 801,182 discloses a scroll type apparatus including two scroll members, each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained at an angular and a radial offset so that the spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces, to thereby seal off and define, along with moving axial contacts between spiral end surfaces and scroll end plates, at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surfaces and, therefore, the fluid pockets change in volume. The volume of the fluid pockets increases or decreases, depending on the direction of the orbiting motion. Therefore, the scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
The principles of operation of a typical scroll type compressor will be described with reference to FIGS. 1a-1d. FIGS. 1a-1d schematically illustrate the relative movement of interfitting spiral elements to compress the fluid, and may be considered as end views of the compressor wherein the end plates are removed and only the spiral elements are shown.
Two spiral elements 1 and 2 are angularly and radially offset and interfit with one another. As shown in FIG. 1a, the orbiting spiral element 1 and fixed spiral element 2 make four line contacts as shown at four points A-D. A pair of fluid pockets 3a, and 3b are defined between line contacts D-C and line contacts A-B as shown by the dotted regions. The fluid pockets 3a and 3b are defined not only by the curved walls of spiral elements 1 and 2 but also by the end plates from which these spiral elements extend. When orbiting spiral element 1 is moved in relation to fixed spiral element 2 so that the center 0' of orbiting spiral element 1 revolves around the center 0 of fixed spiral element 2 with a radius 0--0', while the rotation of orbiting spiral element 1 is prevented, the fluid pockets 3a and 3b shift angularly towards the center of the interfitting spiral elements with the volume of each fluid pocket 3a and 3b being gradually reduced, as shown in FIGS. 1a-1d. Therefore, the fluid in each pocket is compressed.
Pockets 3a and 3b are connected to one another after reaching the stage illustrated in FIG. 1d and, as shown in FIG. 1a, pockets 3a and 3b merge at the center portion 5 and are completely connected to one another to form a single, high pressure central pocket. The volume of the connected single pocket is further reduced by further revolutions of 90.degree., as shown in FIGS. 1b, 1c and 1d. During the course of revolution, outer spaces which open in the state shown in FIG. 1b change as shown in FIGS. 1c, 1d and 1a, to form new sealed off pockets in which fluid is newly enclosed.
Accordingly, if circular end plates are disposed on, and sealed to, the axial facing ends of spiral elements 1 and 2, respectively, and if one of the end plates is provided with a discharge port 4 at the center thereof, as shown in the figures, fluid is taken into the fluid pockets at the radially outer portion and is discharged through the discharge port 4 after compression.
As mentioned above, in the scroll type compressor the fluid is compressed by a change in the volume of the fluid pocket due to orbital motion of the orbiting scroll. The fluid pocket is defined by the line contacts between the curved surfaces of the spiral elements, and the axial contact between the end surfaces of the circular end plates and the axial end surfaces of the spiral elements, the line contacts shifting along the spiral curved surfaces due to the orbital motion. Radial sealing at the line contacts is insured by the use of a compliant drive mechanism, which allows the orbiting scroll to deviate slightly from a perfectly circular orbit so that its spiral element can closely follow the curved surface of the fixed spiral element even if these curved surfaces have dimensional errors. Effective sealing is essential to high volumetric efficiency, especially in the case of the central high pressure space (defined by the line contacts between the spiral surfaces when the two innermost fluid pockets just merge into a single pocket: FIGS. 1d to 1a).
The scroll type fluid displacement apparatus is well-suited for use as the refrigerant compressor of an automobile air conditioner. Generally, it is desirable that the compressor should be compact and light in weight. In particular, the refrigerant compressor for an automobile air conditioner must be compact in size and light in weight because the compressor must fit in the often cramped engine compartment of the automobile. Of course, if the diameter of the compressor is reduced to achieve compactness, the diameter of the circular end plates of the scrolls correspondingly must be reduced as much as possible. In this situation, however, at some portion of the orbital path of the orbiting scroll, the outer terminal end portion of the fixed spiral element will lose axial contact with the surface of the small end plate of the orbiting scroll. Therefore, abnormal wear of the fixed spiral element and the end plate of the orbiting scroll is caused by edgewise interference therebetween. This condition is aggravated when the compliantly driven orbiting scroll is subjected to axial slant, such as often occurs during start-up and shut-down of the compressor. Edgewise interference leading to abnormal wear may also be aggravated when the parallel condition of the end plates is not maintained over the entire swept area of each end plate. In order to avoid this situation, manufacturing tolerances must be kept very close, yielding a costly compressor.